Imaging arrays comprised of multiple sensor pixels 100 are well known in the imaging art. Sensor pixels 100 typically include a switching element 110 such as a thin-film transistor (TFT), and a photoelectric conversion element 120 such as a photodiode. FIG. 1 shows a schematic equivalent pixel circuit for sensor pixels 100. The photoelectric conversion element 120 or photosensor is sensitive to incident radiation and can generate a number of charge carriers where the number depends on the radiation dosage. In imaging arrays including a plurality of pixels, the photogenerated carriers are usually temporarily stored across the internal capacitance of the sensor or in an on-pixel storage capacitor prior to readout. A task of the switching element 110 is to maintain the signal within the pixel and subsequently enable the readout of the signal from the pixel. A signal of interest can be, for example, represented by the change in charge carriers held at a floating node 130 of the pixel, which is typically manifested as a potential change of floating node 130. Aside from the device elements 110, 120, signal lines are also responsible for the functionality of the sensor pixels 100 and the imaging array. The switching element 110 is controlled by scan line 140 that dictates the time and duration of the signal charge release process. Data line 150 provides a path for the released charge carriers to the readout electronics. Bias line 160 provides the appropriate bias voltages for the photoelectric conversion elements 120.
A plurality of sensor pixels can be arranged or tiled in a matrix fashion to form an imaging array. As will be understood to those of ordinary skill in the art, the orientation of the columns and rows is arbitrary, however, for clarity of description it can be assumed that the rows extend horizontally and the columns extend vertically. FIG. 2 shows a schematic equivalent diagram of a 3×3 pixels imaging array that may be used for general radiation detection devices. The bias line 160 is shared among pixels in each column and is coupled to the sensor bias electronics. The data line 150 is shared among pixels in each column and is coupled to the readout electronics. The scan line 140 is shared among pixels in each row and is coupled to the driving electronics. Driving circuitry provides the appropriate signals on scan lines 140 to release the signals stored on the floating nodes 130 of pixels 100 to the data lines 150, for example, one row at a time. The relative waveform timing of the driving electronics, the readout electronics, and the sensor bias electronics may be controlled by an electronic processor (not shown).
For large size imaging arrays, a-Si:H TFT is typically used as the switching element 110. To those of ordinary skill in the art, it is immediately evident that there are numerous other possible choices for the switching elements 110 as well as types of materials that can compose the elements. Due to constraints imposed by the fabrication process of the a-Si:H TFT, there are a number of parasitics associated with the fabricated TFT; these parasitics may sometimes impact the performance of the imaging array and there is a general desire to reduce or minimize their effects.